Visually guided obstacle avoidance in the box jellyfish Tripedalia cystophora and Chiropsella bronzie

Abstract

SUMMARY Box jellyfish, cubomedusae, possess an impressive total of 24 eyes of four morphologically different types. Two of these eye types, called the upper and lower lens eyes, are camera-type eyes with spherical fish-like lenses. Compared with other cnidarians, cubomedusae also have an elaborate behavioral repertoire, which seems to be predominantly visually guided. Still, positive phototaxis is the only behavior described so far that is likely to be correlated with the eyes. We have explored the obstacle avoidance response of the Caribbean species Tripedalia cystophora and the Australian species Chiropsella bronzie in a flow chamber. Our results show that obstacle avoidance is visually guided. Avoidance behavior is triggered when the obstacle takes up a certain angle in the visual field. The results do not allow conclusions on whether color vision is involved but the strength of the response had a tendency to follow the intensity contrast between the obstacle and the surroundings (chamber walls). In the flow chamber Tripedalia cystophora displayed a stronger obstacle avoidance response than Chiropsella bronzie since they had less contact with the obstacles. This seems to follow differences in their habitats.

Pattern and contrast dependent visual response in the box jellyfish Tripedalia cystophora

“…The results presented here clearly demonstrate that the visually guided obstacle avoidance behaviour described for cubomedusae (Garm et al, 2007b) is dependent on actual detection of the obstacle using spatial information and is not a mere positive phototaxis. When we presented T. cystophora medusae with a visual scene without spatial information, the behaviour disappeared even though the overall brightness of the wall equalled that of a scene with stripes resulting in many avoidances.…”

“…In the case of the upper lens eye, the use of spatial information is confirmed by the navigation behaviour, where they see the direction to the canopy (Garm et al, 2011). The obstacle avoidance behaviour also indicates the use of spatial information and true image formation, in that its onset has been shown to be correlated with the size of the obstacle on the retina (Garm et al, 2007b). Still, because the obstacles were dark on a bright background, the behaviour could also have been triggered by a directional drop in light intensity when approaching the obstacles, and thus be part of a simpler positive phototaxis.…”

“…The swim pattern during the last 2.5 min with each visual scene was recorded from above using a video camera (Sony Handycam DCR-HC40, Sony, Tokyo, Japan). The timing equals that used in earlier experiments (Garm et al, 2007b).…”

“…Every morning they have to navigate back to their habitat between the roots, which they do by visually detecting the mangrove canopy through the water surface (Garm et al, 2011). The medusae are also able to detect and avoid obstacles in their surroundings (like the prop roots) and for this they probably use their lower lens eye (Garm et al, 2007b).…”

Assembly of the cnidarian camera-type eye from vertebrate-like components

“…For example, Cubozoa (known as ''box jellyfish'') have camera-type eyes with cornea, lens, and retina; unexpectedly, the cubozoan retina has ciliated PRCs that are typical for vertebrate eyes (7)(8)(9). Cubomedusae are active swimmers that are able to make directional changes in response to visual stimuli (10). The cubozoan jellyfish, Tripedalia cystophora (Fig.…”